Historical Notes: While in London in 1786, Jefferson purchased his first achromatic telescope from Peter and John Dollond, who continued to make the instrument perfected by their father, John Dollond (1706-1761). This refracting telescope, with "three object glasses," cost £10-10.[2] Jefferson acquired a second Dollond telescope for an unknown price in 1793.2 Both instruments survive, although it has not been determined which was purchased first.

In 1793 Jefferson acquired the most valuable instrument in his collection, an equatorial telescope by Jesse Ramsden (1735-1800), whom he considered preeminent among makers. With "this noble instrument," as he called it, he fixed the meridian at Monticello and viewed the solar eclipse of 1811.[3] Judged by one scholar to be "unquestionably the most sophisticated instrument in the United States" at the time, Jefferson's equatorial was the foundation of his favorite theory of a method for determining longitude by lunar distances without at timepiece.[4]

Although he often expressed a desire for a more powerful telescope, Jefferson apparently never acquired one capable of viewing the eclipses of Jupiter's satellites, a requisite for the other common method of determining longitude.

In the 1820s Jefferson lent his "best" telescope to Hermann Böÿe, then engaged in mapping Virginia. When attempting to recover it, he wrote that he intended to give it to the University of Virginia.[5] The telescope illustrated here descended through the family of Thomas Jefferson Randolph and bears the inscription "Thomas Jefferson Monticello" on the band near the eyepiece.

1784 November 11. (Jefferson to David Rittenhouse). "The Abbe Rochon has lately made a very curious discovery in optics. He has made lenses with a chrystal from Iceland which have a double focus, perfectly distinct and at considerable distances from each other. I looked thro' a telescope to which he had adapted one of these and saw at the same instant an object on the banks of the Seine and a house half a mile further back with equal precision, the intermediate objects being dim as not at a proper distance for either focus."[8]

1786 January 25. (Jefferson to David Rittenhouse). "In a letter to Mr. Hopkins I mentioned to him that the Abbe Rochon, who discovered the double refracting power in some of the natural chrystals, had lately made a telescope with the metal called Platina, which while it is susceptible of as perfect a polish as the metal heretofore used for the specula of telescopes, is inattackable by rust as gold and silver are."[9]

1787 January 30. (Jefferson to James Madison). "I send you by Colo. Franks your pocket telescope, walking stick, and chemical box. The two former could not be combined together."[10]

1792 December 26. (Jefferson to John Jones). "Martin in his 3d. Philosophic Britannica pg. 369. speaks much in favor of his new Reflecting Pocket telescope with a Megaloscope, sufficient to show Jupiter's moons. Has it been brought into use? How has it answered and what is it's price? Dr. Maskelyne in the Ephemeris page 154. speaks of [Dolland's] refracting telescope with 3. objects glasses, of 46. I[nches]. focal length, which he says is equal to those of 10. feet with a double object glass. The price..."[11]

1793 March 9. (William & Samuel Jones to Jefferson). "Mr. Martin very recommends those alterations to the telescope as being himself in this way sometimes of making them. It is undoubtedly a curious contrivance but interferes too much with the construction of the instrument subjecting it to be deranged, and to be out of order, somewhat, in shifting occasionally the parts. None of these construction are now made, but we could easily make you one if desired. The length would be 9 Inches, mounted in brass, and to be used occasionally with or without the stand. The price will be either 4 or 5 guineas, not more, a; a pocket fish case included. Jupiter's Moons and Saturn's Ring can be distinctly seen by them. A 12 Inch reflector, would be much more perfect, and magnify more, but not suitable for the pocket. The price of such a one will be 7 Guineas. The 3 1/2 feet achromatic refractor, is the best kind of achromatic telescope that can be made. The price is 16 Guineas. If with a brass tube, and rack work 22 Guineas. If the micrometrical and other apparatus the price is from 30 to 70 Guineas."[12]

1793 March 10. (Alexander Donald to Jefferson). "The Blackguard Ramsden has disappointed me in not having gotten ready the Telescope which he faithfully promised would be ready two months ago. I must get one from Dolland."[13]

1793 November 14. (Jefferson to William Mewbern). "Mr. Donald of London, in a letter of August 30. informs me you had been so kind as to take charge of a telescope for me. Instead of sending it on to Philadelphia, delver it to Mr. Randolph my son in law whenever he may happen to be in Richmond, or to his order."[14]

1801 May 18. (Thomas Claxton to Jefferson). "I, long since, intend to procure a good Spy Glass, which I think is much wanting for the convenience of the House..."[15]

1801 June 24. (Benjamin Vaughan to William Vaughan). "[Jefferson] is desirous of a refracting telescope, suited both for terrestrial and celestial objects, and costing him 20 to 30 guineas."[16]

1807 July 2. (William Small to Jefferson). "And an engine for cutting Male and female screws, on and in tubes, altho near completed, yet is unfinished--the assistance of that instrument would in 20 minuets [sic] complete your telescope, I expect much to your satisfaction--If it is got done to day I will forward by may lad your orders immediately after--the other work haveing been done a few hours after recieving it, there is not other hinderance."[17]

1809 May 18. (Jefferson to George Jefferson). Missing trunk forwarded from Richmond (one with Indian vocabularies) contained "a pocket telescope with a brass case."[18]

1813 December 4. (Jefferson to Abbe Rochon). "I received at the same time your pamphlet on the Micrometer of rock-chrystal, the advantages of which you had shewn to me in 1785 at Dr. Franklin's at Passy, on the telescope you gave him, which is now in my possession."[19]

1814 January 18. (William Short to Jefferson). "I have received from the Abbe Rochon a micrometer of his invention--and also a telescope of Platina...I should be very glad to show you the mircometer, as I think it would interest you."[20]

1819 February 2. (Jefferson to William Davenport). "I some time ago forwarded a telescope to Doctor Robert Patterson with a request to put it into good hands to be repaired: he informs me he delivered it to you, and that the price for repairing it for land observations (which will be sufficient) will be 10. dollars...You will have seen that the only method of advancing or withdrawing the movable tube was by hand. This being inconvenient a workman, not very dexterous, undertook to make it moveable by tooth and pinion wheels, in which he failed entirely. Should this be now practicable I should greatly prefer it and would remit in the same way any additional charge it may incur. When done, I will pray you to have it put into an outer box, and forwarded by some of the vessels bound from Philadelphia to Richmond..."[22]

1822 August 29. (Jefferson to Thomas Skidman). "But in the case of the heavenly bodies, we can have no such aid [auxiliary light concentrated on the object]. The moon, for example, receives from the sun but a fixed quantity of light. In proportion as you magnify her surface, you spread that fixed quantity over a greater space, dilute it more, and render the object more dim. If you increase her magnitude infinitely, you dim the face infinitely also, and she becomes invisible...Hershel has availed himself of the properties of the parabolic mirror to the point beyond which its effect would be countervailed by the diminution of light on the object. I barely suggest this element, not presented to view in your letter, as one which must enter into the estimate of the improved telescope you propose."[25]

1826 January 3. (Jefferson to William Short). "I lent him [Mr. Boye] him a fine Borda's circle of reflection 2. or 3. years ago and my best telescope."[26]

Footnotes

↑ Jefferson to David Rittenhouse, Monticello, August 12, 1792, in PTJ, 24:287-288; Jefferson, January 5, 1793, in MB, 2:888; Jefferson to William Lambert, Monticello, November 29, 1822, in L&B, 15:347.

↑ Jefferson to William Short, January 3, 1826. Thomas Jefferson Papers, Massachusetts Historical Society. A second pedestal achromatic telescope made by Peter and John Dollond that is owned by the University of Virginia may have been deposited there according to Jefferson's intention. It has been on loan to the Thomas Jefferson Foundation since 1949.